The invention relates to a war indicator for friction linings for vehicle brakes.
A tractor or motorized excavation machinery, for example, an agricultural tractor, a loader, a dumper of an excavator, is often used off road and thus dirt and mud, water or snow can cover the wheels and form thick coatings on the wheels covering the wheel hubs. The law and security considerations dictate that all motor vehicles and in particular heavy vehicles must have well functioning brakes. It is therefore important, despite the heavy coating of dirt on the wheel hubs, to be able to check the wear situation for each friction lining in the vehicle without having to disassemble the brakes or drive to the shop for checking.
Wear indicator based on electrical, electronical or mechanical principles are previously known but are unreliable, and the first two mentioned tend not to function at all under the hard operating conditions described above. Another disadvantage is that the driver is first alerted when the friction lining in question is almost completely worn down, for example by an electrical circuit being broken. In principle, the lining is then worn down to a maximum permissible thickness determined by the manufacturer, which means that the vehicle should no longer be driven until new linings have been installed.
A conventional mechanical method of measuring brake wear is by measuring, through a cavity in the flange of the axle casing and in the brake piston, with a special tool against the countersurfaces and discs of the brake, and comparing these measurements to calculate the thickness of the lining. Since vehicles of this type usually have oil-cooled brakes, the cavity in the axle casing must be replugged after each measurement and transmission oil runs out through the cavity during the measuring process.
Another method of conventional type is making a radial opening in the hub retainer directly in front of the peripheral edge of the brake disc. For the same reasons as discussed above, the opening is normally replugged. The distance between the countersurface and the brake piston in a portion located outside the peripheral edge of the brake disc is measured with a type of feeler gauge, which is inserted through the radial opening. An additional disadvantage of this method is that the radial opening in some vehicles is covered by the wheel rim, which means that the wheel must be taken off prior to each measurement.
A further developed mechanical variant has an easily displaceable rod built into the brake, with the aid of which it is possible to measure the position of the brake piston relative to the brake housing when the brake is engaged. Conventionally, this pin has a fixed length which is a disadvantage as it means that the measured distance varies depending on the tolerances of the components affecting the length of the protruding pin. Such components can be the brake housing, the piston, the discs, the stationary discs and the counter surface. The two previously described methods also have this disadvantage.